I created a File > New > Seam Web Project using Seam 2.0 and JBoss 4.2. Once the project is created, Eclipse reports "cannot be resolved to a type" errors in the Authenticator.java as if jboss-seam.jar weren't in the classpath.

In the status bar, it says:

Classpath entry /MyProject/EarContent/jboss-seam.jar will not be exported or published. Runtime ClassNotFoundException may result.

If I add jboss-seam.jar to the classpath, that warning moves to the Problems tab and the errors go away. If I then remove it, the warning also goes away and everything is as it's supposed to be in the beginning.